Yoke compartment of voice coil motor for hard disk drive and voice coil motor using said yoke compartment

ABSTRACT

A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, includes a first step of subjecting the yoke component to a barrel polishing treatment; and a second step of subjecting the yoke component to at least one of an abrasive grain fluidization treatment, a thermal deburring treatment, a magnetic polishing treatment, an ultrasonic deburring treatment, and a water jet deburring treatment.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a yoke component for making up amagnetic circuit of a voice coil motor for a hard disk drive, and amethod of deburring the surface of the yoke component, and particularlyto a method of deburring a yoke component, which is capable of removingburrs produced on all ridge lines, including ridge lines at finelymachined portions, of the yoke component. The present invention alsorelates to a voice coil motor for a hard disk drive, using the yokecomponent from which burrs are thus removed.

[0002] A voice coil motor for a hard disk drive includes, as shown inFIG. 1, a rare-earth magnet “a” and a yoke component “b” for making up amagnetic circuit of the voice coil motor. In addition, character “c”designates a coil. In recent years, along with a tendency to increasethe storage capacities of hard disks, flying heights of magnetic headshave come to be reduced, and to prevent occurrence of head crush due tothe reductions in flying heights of the magnetic heads, voice coilmotors have been increasingly required to be cleaned.

[0003] Of components of a voice coil motor, a yoke componentmanufactured by pressing or cutting has a disadvantage that it has highviscosity causing shearing burrs or cutting burrs. This is because theyoke component is mainly made from a low carbon steel having a hightoughness for obtaining an excellent motor performance.

[0004] Further, in recent years, since hard disk drives have beenminiaturized, yoke components for making up magnetic circuits of voicecoil motors used for the hard disk drives have come to be miniaturizedand to be complicated in shape. As a result, the number of yokecomponents having finely machined portions such as through-holes, bends,and threaded holes has been increased, thereby tending to increase thefrequency of occurrence of burrs. For example, in a yoke component thusminiaturized and complicated in shape, shearing burrs or cutting burrsof 0.5 mm or less in thickness are often produced in through-holes orthreaded holes of about 3 mm in diameter. These burrs adhering on thesurface of the yoke component do not necessarily remain adhering thereonbut may be easily dropped therefrom due to physical or chemical causes.

[0005] Even if burrs are not dropped from the surface of a yokecomponent, since the surface of the yoke component is subjected tonickel plating, the nickel plating film on the surface may be crushedand a nickel powder be dropped therefrom when an external impact forceis applied to the burrs.

[0006] The drop of burrs leads to deterioration of the cleanness of avoice coil motor for a hard disk drive, and further causes head crushand the like if the dropped burrs collide with a magnetic head uponoperation of the hard disk drive. In particular, since the flying heightof a magnetic head has been recently reduced to 0.1 μm or less, the dropof burrs of 0.5 mm or less in thickness has become a cause of headcrush.

[0007] If a dropped burr adheres on a hard disk, there arises a problemassociated with breakage of data recorded in the hard disk because ofthe ferromagnetic property of the burr. In recent years, since therecording density of a hard disk has become 1 GB/cm² or more, the dropof a burr of about 0.5 mm in thickness has possibly led to seriousbreakage of data recorded in the hard disk.

[0008] To remove burrs on yoke components for making up magneticcircuits of voice coil motors for hard disk drives, various kinds ofdeburring methods have been proposed; however, any one of these methodshas not succeeded to perfectly remove burrs on yoke components. Forexample, a deburring method using a barrel polishing treatment iseffective to remove large burrs produced on ridge lines around the outerperiphery of a yoke component; however, such a method is disadvantageousin that burrs of 0.5 mm or less in thickness present on finely machinedportions, such as through-holes, bends, and threaded holes, of the yokecomponent cannot be removed because abrasive grains do not sufficientlycollide therewith.

[0009] A burring method using a chemical polishing treatment iseffective to remove micro-burrs of 0.1 mm or less in thickness presentat any location of a yoke component; however, such a method isdisadvantageous in that burrs of more than 0.1 mm and 0.5 mm or less inthickness present on a yoke component cannot be removed by dissolutionbecause of a possibility that longer chemical polishing may dissolve themain body of the yoke component. In general, the chemical polishingtreatment is additionally used to make small burrs of 0.5 mm or lesspresent on finely machined portions such as through-holes, bends, orthreaded holes, which burrs cannot be removed by barrel polishingbecause the abrasive grains are larger in size than the finely machinedportions, and as described above, the chemical polishing treatment hasnot effect of perfectly removing such burrs of 0.5 mm or less.

[0010] A deburring method using an abrasive grain fluidization treatmentis effective to remove whisker-like burrs having fine roots, producedtypically upon cutting of a yoke component, by pressing viscoelasticmedia containing abrasive grains kneaded therein to burrs; however, sucha method is disadvantageous in that burrs produced by shearing, whichhave roots wider than tips, cannot be perfectly removed at the roots.Further, a deburring method using a thermal deburring treatment isdisadvantageous in that heat generated at burrs are easy to propagate tothe main body of a yoke component, thereby making it difficult to removethe burrs by oxidation; a deburring method using a magnetic polishingtreatment is disadvantageous in that even if needle media made from aferromagnetic material collide with a burr, the burr cannot be removedat the root; and a deburring method using ultrasonic vibration or waterpressure is disadvantageous in that burrs produced by shearing cannot beremoved at the roots, and therefore, these methods are not generallyused for deburring yoke components for making up magnetic circuits ofvoice coil motors for hard disk drives.

[0011] A prior art deburring method has generally used only the barrelpolishing treatment or the barrel polishing treatment followed by thechemical polishing treatment to deburr yoke components for making upmagnetic circuits of voice coil motors for hard disk drives; however,such a method has failed to remove burrs of 0.5 mm or less in thicknesspresent on finely machined portions, such as through-holes, bends, andthreaded holes, of a yoke component, and in some cases, the prior artmethod has adopted brushing to remove such burrs.

[0012] The brushing for finely machined portions on which fine burrs areproduced, however, is difficult to be automated because the shapes ofyoke components differ for each voice coil motor, and therefore, suchbrushing must be manually performed, to cause a problem in that thedeburring cost is raised.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to provide a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which yoke component has no burr on all ridge lines,particularly, ridge lines at finely machined portions, of the yokecomponent; to provide a method of deburring a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichis capable of certainly, efficiently deburring the yoke component; andto provide a voice coil motor for a hard disk drive, using a yokecomponent from which burrs are thus removed.

[0014] The present inventor has made examination to achieve the aboveobject, that is, to certainly, efficiently deburr a yoke component madefrom a low carbon steel on which burrs are produced upon shearing orcutting work of the yoke component, and found that burrs present on allridge lines, particularly, ridge lines at finely machined portions (forexample, through-holes, threaded holes and recesses, each of which hasan diameter of 10 mm or less, and further bends each having a radius ofcurvature of 5 mm or less) are difficult to be removed only by a barrelpolishing treatment because abrasive grains cannot be sufficientlycollide with the burrs present on the finely machined portions; however,these burrs present on all ridge lines of the yoke component can becertainly removed by subjecting the yoke component to the barrelpolishing treatment, and then subjecting the yoke component to at leastone of a thermal deburring treatment, a magnetic polishing treatment, anultrasonic deburring treatment, and a water jet deburring treatment. Thepresent inventor has thus accomplished the present invention on thebasis of the above-described knowledge.

[0015] Therefore, according to a first aspect of the present invention,there is provided a yoke component, made from a low carbon steel, formaking up a magnetic circuit of a voice coil motor for a hard diskdrive, wherein the yoke component has on any ridge line thereof no burrof 0.5 mm or less in thickness.

[0016] According to a second aspect of the present invention, there isprovided a deburring method of removing burrs present on the surface ofa yoke component, made from a low steel carbon steel, of a voice coilmotor for a hard disk drive, including: a first step of subjecting theyoke component to a barrel polishing treatment; and a second step ofsubjecting the yoke component to at least one of an abrasive grainfluidization treatment, a thermal deburring treatment, a magneticpolishing treatment, an ultrasonic deburring treatment, and a water jetdeburring treatment.

[0017] According to a third aspect of the present invention, there isprovided a voice coil motor for a hard disk drive, including: a yokecomponent, made from a low carbon steel, for making up a magneticcircuit of the voice coil motor, wherein the yoke component has on anyridge line thereof no burr of 0.5 mm or less in thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic perspective view of a voice coil motor;

[0019]FIGS. 2A and 2B are views typically showing two kinds of forms ofburrs present on a yoke component, wherein FIG. 2A shows a shearing burrproduced on a yoke component upon pressing work of the yoke component,and FIG. 2B shows a whicker-like burr produced on a yoke component uponcutting work of the yoke component; and

[0020]FIGS. 3A to 3D are views typically showing steps of removing burrspresent at the opening edge of a through-hole of a yoke component,wherein FIG. 3A shows a state before barrel polishing; FIG. 3B shows astate after barrel polishing; FIG. 3C shows a state after abrasive grainfluidization treatment; and FIG. 3D shows a state after chemicalpolishing.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Burrs to be removed by a deburring method of the presentinvention are burrs of 0.5 mm or less in thickness produced on all ridgelines, particularly, ridge lines at finely machined portions, of a yokecomponent made from a low carbon steel for making up a magnetic circuitof a voice coil motor for a hard disk drive. FIGS. 2A and 2B are viewstypically showing two kinds of forms of burrs and defining a thicknessof each burr, wherein FIG. 2A shows a shearing burr produced on a yokecomponent upon pressing work of the yoke component, and FIG. 2B shows awhisker-like burr produced on a yoke component upon cutting work of theyoke component. The forms of burrs to be removed by the deburring methodof the present invention, however, are limited thereto.

[0022] The deburring method of the present invention includes: (1) afirst step of subjecting a yoke component, on which burrs of theabove-described forms are present, to a barrel polishing treatment; and(2) a second step of subjecting the yoke component to at least one of anabrasive grain fluidization treatment, a thermal deburring treatment, amagnetic polishing treatment, an ultrasonic deburring treatment, and awater jet deburring treatment. Additionally, the deburring method of thepresent invention may include (3) a third step of subjecting the yokecomponent to a chemical polishing treatment as needed.

[0023] Hereinafter, each of the above-described treatments of thedeburring method of the present invention will be described.

[0024] Deburring Step by Barrel Polishing Treatment

[0025] The deburring by barrel polishing treatment is intended to removeburrs on ridge lines with which abrasive grains can sufficientlycollide, other than burrs on ridge lines at finely machined portionssuch as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive. The barrel polishing treatment is also intended to make abrasivegrains collide to shearing burrs of 0.5 mm or less in thickness atfinely machined portions such as through-holes, bends, andthreaded-holes, to forcibly roll the burrs and make thin the rootsthereby by collision of the abrasive grain which is insufficient toremove the burrs, thereby forming the burrs into shapes easy to beremoved at the subsequent step using at least one of the abrasive grainfluidization treatment, a thermal deburring treatment, a magneticpolishing treatment, an ultrasonic deburring treatment, or a water jetdeburring treatment.

[0026] The barrel polishing treatment can be performed by charging ayoke component, abrasive grains mainly made from alumina, silica, ormagnesia, and water to which a rust-preventive solution is added, into arotary barrel, vibration barrel, or centrifugal barrel, and making theabrasive grains collide the yoke component by rotation or vibration. Theshape of each abrasive grain may be a spherical or triangular shape, andthe size of each abrasive grain may be 3 mm or more, particularly, 5 mmor more and 20 mm or less, particularly, 15 mm or less, and generally beabout 10 mm. It may be undesirable to use abrasive grains each having asize smaller than that described above, that is, less than 3 mm. This isbecause such small abrasive grains may remain in threaded holes orrecesses. The barrel polishing treatment can remove burrs, each having athickness ranging from 0.5 mm to 1.0 mm, produced on ridge lines withwhich abrasive grains can sufficiently collide along various directions,other than burrs produced at finely machined portions such asthrough-holes, bends, and threaded holes, of the yoke component. Thebarrel polishing treatment, however, cannot remove but only rollshearing burrs of 0.5 mm or less in thickness produced at finelymachined portions such as through-holes, bends, and threaded holesbecause abrasive grains collide with the burrs along limited directions.Here, as the effect of the barrel polishing treatment, although theshearing burrs of 0.5 mm or less cannot be removed by the barrelpolishing treatment, the roots thereof become thinner than those of theoriginal burrs before barrel polishing, and therefore, such burrs areeasy to be removed at the subsequent step using at least one of theabrasive grain fluidization treatment, a thermal deburring treatment, amagnetic polishing treatment, an ultrasonic deburring treatment, or awater jet deburring treatment.

[0027] According to the prior art deburring method, shearing burrs of0.5 mm or less in thickness produced at finely machined portions, suchas through-holes, bends, and threaded holes, of a yoke component, whichcannot be removed by the barrel polishing treatment, are left as theyare or are made smaller by additional chemical polishing. It should benoted that as described above, the additional chemical polishing failsto perfectly remove the shearing burrs of 0.5 mm or less which haveremained after barrel polishing.

[0028] Deburring Step by Abrasive Grain Fluidization Treatment

[0029] The deburring by abrasive grain fluidization treatment isintended to remove burrs of 0.5 mm or less produced at finely machinedportions, such as through-holes, bends, and threaded holes, of a yokecomponent for making up a magnetic circuit of a voice coil motor for ahard disk drive, which burrs cannot be removed by barrel polishing.

[0030] The abrasive grain fluidization treatment is performed bymechanically pressing special clay-like viscoelastic media containingabrasive grains kneaded therein to a portion to be deburred, therebydeburring the portion. In this case, the elastic effect of theviscoelastic media is added to the abrasive grains kneaded therein, toproduce a polishing pressure and a moving speed of abrasive grainsnecessary for polishing the portion to be deburred. In this treatment,there is used an apparatus capable of pressing the viscoelastic media inboth the upward and downward directions, to reciprocally move the media,thereby enhancing the deburring ability.

[0031] In the case of removing burrs present at finely machinedportions, such as through-holes, bends, and treaded holes, of a yokecomponent for making up a magnetic circuit of a voice coil motor for ahard disk drive by using the above-described apparatus, a flow passageto fluidize the media to the portion to be deburred is formed inmatching to the portion to be deburred by using a jig. In this case, forenhancing the mass-productivity by simultaneously performing theabrasive grain fluidization treatment to a plurality of yoke components,flow passages may be formed by the jigs in such a manner as to bematched to the plurality of yoke components laminated to each other. Theviscoelasticity of the media is not particularly limited but may bepreferably not high so much if the media is used for removing burrs of0.5 mm or less present at finely machined portions, such asthrough-holes, bends, and treaded holes, of a yoke component for makingup a magnetic circuit. To easily remove the media from a yoke componenthaving been subjected to abrasive grain fluidization, fat and oil may bepreviously contained in the media. The material of the abrasive grainskneaded in the media may be selected from silicate carbide, boroncarbide, or diamond, and the particle size thereof is selected in arange of #50 to #500 in accordance with the production state of burrs tobe removed. The pressure may be selected in a range of 10 to 100 kg/cm²in accordance with the production state of burrs to be removed. Sincethe through-holes, threaded holes, or recesses are filled with the mediaafter the deburring by abrasive grain fluidization, the media isrequired to be removed therefrom by air cleaning or water cleaning. Withthis abrasive grain fluidization treatment, shearing burrs of 0.5 mm orless in thickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless cannot be removed by the prior art single abrasive grainfluidization treatment.

[0032] Whisker-like burrs having fine roots, which are produced atfinely machined portions, such as threaded holes or recesses, uponcutting work of a yoke component, can be perfectly removed by collisionof the abrasive grains therewith during the abrasive grain fluidizationtreatment.

[0033] The apparatus used for the abrasive grain fluidization treatmenthas been described in [“Deburring Method Using Abrasive GrainFluidization Treatment”, Mechanical Technology, Vol. 36, No. 9 (theAugust Number in 1988), Nikkan Kogyo Shinbunsha K. K.].

[0034] If the deburring by abrasive grain fluidization is performedwithout barrel polishing as the previous step, as described above,shearing burrs which have roots wider than tips cannot be removed at theroots even if the viscoelastic media containing abrasive grains kneadedtherein are pressed to the burrs, and therefore, shearing burrs on allridge lines, including burrs at finely machined portions, cannot beremoved at all.

[0035] Deburring Step by Thermal Deburring Treatment

[0036] The deburring by thermal deburring treatment is intended toremove burrs of 0.5 mm or less produced at finely machined portions,such as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which burrs cannot be removed by barrel polishing.

[0037] The thermal deburring treatment is performed by putting yokecomponents in a gastight combustion chamber, gastightly closing thecombustion chamber, and feeding a compressed combustion gas in thecombustion chamber through a burnable gas inlet. The feed pressure ofthe combustion gas may be set in a range of 3 to 10 atm in accordancewith the number of yoke components and the production state of burrs tobe removed. To avoid deformation of yoke components, the feed pressureof the combustion gas may be set at a value being as small as possible.The composition of the combustion gas is represented by CH₄:O₂=1:2.5.That is to say, the combustion gas contains oxygen in an amount largerthan that necessary for combustion of methane. The excess oxygen isconsumed for combustion of burrs. Accordingly, the optimum mixing ratioof the combustion gas may be set at a value matched to the productionstate of burrs in order to prevent part of the burrs from remaining dueto the lack of combustion by insufficient oxygen or to avoid significantoxidation of the main body of the yoke component due to excess oxygen.

[0038] When the combustion gas supplied in the combustion chamber isignited by an ignition plug, such a combustion gas is instantly burned,to cause heat waves of about 3000° C., thereby removing burrs byoxidation. At this time, the surface of the main body of the yokecomponent is slightly oxidized to form an oxide film. Such an oxide filmmay be desirable to be removed by acid cleaning or the like after thethermal deburring treatment. With this thermal deburring treatment,shearing burrs of 0.5 mm or less in thickness present at finely machinedportions, particularly, at through-holes and bends formed by punchingcan be removed in combination with the effect of the previous step usingbarrel polishing, that is, the effect of forcibly rolling the burrsthereby making thin the roots thereof. It should be noted that the aboveshearing burrs of 0.5 mm or less cannot be removed by the prior artsingle thermal deburring treatment.

[0039] Whisker-like burrs having fine roots, which are produced atfinely machined portions, such as threaded holes or recesses, uponcutting work of a yoke component, can be perfectly oxidized and removedby the thermal deburring treatment.

[0040] The thermal deburring apparatus has been described in [“InstantDeburring by Using Thermal Impact”, Mechanical Technology, Vol. 29, No.8, pp. 135-137 (1981)].

[0041] If the thermal deburring treatment is performed without barrelpolishing as the previous step, as described above, shearing burrs whichhave roots wider than tips cannot be removed by oxidation because heatgenerated at the burrs is easy to propagate to the main body of the yokecomponent, and therefore, shearing burrs on all ridge lines, includingburrs at finely machined portions, cannot be removed at all.

[0042] Deburring Step by Magnetic Polishing Treatment

[0043] The deburring by magnetic polishing treatment is intended toremove burrs of 0.5 mm or less produced at finely machined portions,such as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which burrs cannot be removed by barrel polishing.

[0044] The magnetic polishing treatment is performed as follows: First,ferromagnetic stainless steel media in the forms of needles each havinga diameter of 0.2 to 1.0 mm and a length of about 5 mm and parts to bedeburred are put in a vessel. At this time, a cleaning solution forpreventing the parts to be deburred and the media from beingcontaminated is simultaneously poured in the vessel. The vessel is putin a magnetic field in which N and S poles are alternately changed. Asthe polarities of the magnetic field are quickly changed from eachother, the ferromagnetic media are repeatedly, strongly stirred andvibrated, and are inserted in finely machined portions such asthrough-holes, bends, and threaded holes, to thereby remove burrs bycollision therewith. As a method of changing the N and S poles in themagnetic field in the vessel from each other, there may be adopted amethod of disposing the vessel between electric magnets to which analternating current is applied, or a method of rotating a disk, on whichstrong magnets are provided with N and S poles alternately arranged, ata high speed under a base on which the vessel is mounted.

[0045] In general, parts to be deburred by magnetic polishing arenon-magnetic bodies. Ferromagnetic parts are difficult to be deburred bymagnetic polishing because such parts are moved in the same direction asthat of the ferromagnetic media when the N and S poles in the magneticfield are changed from each other. However, by fixing ferromagneticparts in a vessel by means of non-magnetic jigs, the media are allowedto strongly collide with the ferromagnetic parts, thereby removing burrspresent thereon.

[0046] A yoke component is a ferromagnetic body made from a low carbonsteel. Accordingly, by fixing the yoke component by means of a jig,burrs present on the yoke component can be removed by magneticpolishing. In this case, to make the media certainly collide with theyoke component, the yoke component may be desirable to be fixed with itsshearing direction directed in parallel to the direction of the magneticfield.

[0047] The charged amount of yoke components is determined in accordancewith the size of a vessel in which the yoke components are to be put,and the design of jigs for fixing the yoke components. The frequency forchanging the polarities of a magnetic field in the vessel is set at50-60 Hz or more for strongly stirring and vibrating the media, and thechange in polarities of the magnetic field at a high frequency can beeasily performed by adopting the method of rotating a disk, on whichstrong magnets are provided with N and S poles alternately arranged, ata high speed under a base on which the vessel is mounted.

[0048] The thickness of each of the media may be selected in a range ofabout 0.5 to 1.0 mm in accordance with the production state of burrs of0.5 mm or less in thickness present at finely machined portions, such asthrough-holes, bends, and thread holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing. The use of the media eachhaving a thickness of about 0.2 mm reduces the deburring effect becauseof the light weights of the media. Such fine media are generally usedfor deburring resin based parts.

[0049] The polishing time is set in a range of about 1 to 10 min inaccordance with the production state of burrs, and the frequency forchanging the polarities of a magnetic field. Since the surface of theyoke component is wet and is thereby liable to be rusted after magneticpolishing, it may be desirable to wash the yoke component with water forremoving the cleaning solution therefrom, and to dry the yoke componentby using an oven or air blower.

[0050] With this magnetic polishing treatment, shearing burrs of 0.5 mmor less in thickness present at finely machined portions, particularly,at through-holes and bends formed by punching can be removed incombination with the effect of the previous step using barrel polishing,that is, the effect of forcibly rolling the burrs thereby making thinthe roots thereof. It should be noted that the above shearing burrs of0.5 mm or less produced by punching cannot be removed by the prior artsingle magnetic polishing treatment.

[0051] Whisker-like burrs having fine roots, which are produced atfinely machined portions, such as threaded holes or recesses, uponcutting work of a yoke component, can be perfectly removed by collisionof the media therewith during the magnetic polishing treatment.

[0052] The magnetic polishing apparatus has been described in [“MagneticPolishing Method Capable of Removing Micro-Burrs on Product withoutDeformation and Efficiently Finishing the Product” [b (2)] JA G0937ATool Engineer (JPN) 38[2] 34-39 ('97)].

[0053] If the magnetic polishing is performed without barrel polishingas the previous step, as described above, shearing burrs which haveroots wider than tips cannot be removed at the roots even if the mediacomposed of ferromagnetic needles collide with the burrs during themagnetic polishing treatment, and therefore, shearing burrs on all ridgelines, including burrs at finely machined portions, cannot be removed atall.

[0054] Deburring Step by Ultrasonic Deburring Treatment

[0055] The deburring by ultrasonic deburring treatment is intended toremove burrs of 0.5 mm or less produced at finely machined portions,such as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which burrs cannot be removed by barrel polishing.

[0056] The ultrasonic deburring treatment is performed by putting a yokecomponent to be deburred in water, and emitting strong ultrasonic wavesinto the water, to impart strong vibration to burrs on the yokecomponent by making use of cavitation (growth and extinction ofmicro-bubbles) in the resonance region of the ultrasonic waves, therebyremoving the burrs thus fatigued by vibration. The resonance region inwhich cavitation occurs is limited to a specific area calculated by thefrequency of the ultrasonic waves, and therefore, a location to bedeburred may be desirable to be fixed in the specific area.

[0057] In the case of deburring a plurality of locations of a yokecomponent, the yoke component suspended from a jig into water may beswung. The frequency of the ultrasonic waves used for this ultrasonicdeburring treatment may be as low as about 25 kHz. The use of theultrasonic waves having a frequency more than 30 kHz increases theresonance region in water but reduces the cavitation to such an extentas to make impossible the deburring. Meanwhile, the use of ultrasonicwaves having a frequency lower than 20 kHz, which is near audiofrequencies, may cause large noise. Accordingly, the frequency of theultrasonic waves is preferably in a range of 20 to 30 kHz. The output ofan ultrasonic wave generator used for this ultrasonic deburringtreatment may be as high as about 1200 W, and ultrasonic oscillators maybe densely arranged for enhancing the deburring ability. The lower thetemperature of water used for ultrasonic deburring treatment, the higherthe cavitation effect. From this viewpoint, the temperature of waterused for ultrasonic deburring treatment may be controlled at a lowtemperature of 10° C. or less for increasing the cavitation effect.Since oil or air in water obstructs the occurrence of cavitation, theuse of pure water or deaeration before deburring may be carried out forenhancing the deburring effect. The ultrasonic deburring treatment timemay be set in a range of 30 sec to 10 min in accordance with the shapesof burrs. Since the surface of the yoke component is wet and is therebyliable to be rusted after ultrasonic deburring, the yoke component maybe desirable to be dried by using an oven or air blower. With thisultrasonic deburring treatment, shearing burrs of 0.5 mm or less inthickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless cannot be removed by the prior art single ultrasonic deburringtreatment.

[0058] Whisker-like burrs having fine roots, which are produced atfinely machined portions, such as threaded holes or recesses, uponcutting work of a yoke component, can be perfectly removed by vibrationdue to ultrasonic waves.

[0059] The ultrasonic deburring apparatus has been described in[“Precise Surface Finish and Burr Technology-Removal of Burrs andSurface Finish by Ultrasonic Cleaning” [b(2)] JA F145A, MechanicalTechnology, (JPN) 44[(2)]].

[0060] If the ultrasonic deburring is performed without barrel polishingas the previous step, as described above, shearing burrs which haveroots wider than tips cannot be removed at the roots even by vibrationdue to ultrasonic waves, and therefore, shearing burrs on all ridgelines, including burrs at finely machined portions, cannot be removed atall.

[0061] Deburring Step by Water Jet Deburring Treatment

[0062] The deburring by water jet deburring treatment is intended toremove burrs of 0.5 mm or less produced at finely machined portions,such as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which burrs cannot be removed by barrel polishing.

[0063] The water jet deburring treatment is performed by discharging awater jet at a high pressure 100 to 700 kg/cm² from a nozzle to a yokecomponent by a high pressure pump such as a plunger pump, therebyremoving burrs on the yoke component by collision of the water jet withthe burrs. The nozzle may be of a direct-jet type for preventing a waterjet at a high pressure from being spread, and also may have only onedischarge port for increasing the deburring ability at maximum.

[0064] The discharge pressure, distance between the nozzle and a yokecomponent, flow rate of discharged water, and discharge time should beset at such values as not to deform or damage the yoke component.Concretely, to obtain a sufficient deburring effect, the distancebetween the nozzle and the yoke component may be set in a range of 40 to100 mm; the flow rate of the discharge water may be set in a range of 10to 50 L/min, and the discharge time may be set in a range of 1 to 10sec.

[0065] First, a position or positions of one burr or a plurality ofburrs of 0.5 mm or less in thickness at one or a plurality of finelymachined portions, such as through-holes, bends, or threaded holes, of ayoke component, which burr or burrs cannot be removed by barrelpolishing, has or have been previously checked. If one position of theburr has been checked, the yoke component is fixed by means of a jigwith such a position directed to the nozzle, and a water jet at a highpressure is discharged from the nozzle to the position, to therebyremove the burr. If a plurality of positions of the burrs have beenchecked, a water jet at a high pressure can be made to collide with theplurality of burrs on the yoke component by moving one or both of thenozzle and the yoke component. Further, a water jet at a high pressurecan be made to collide with any position of a yoke component by swingingone or both of the nozzle or the yoke component. In the case of movingone or both of the nozzle and a yoke component, the moving speed may beset at a value being as low as 20 mm/sec or less. If the moving speed ismore than 20 mm/sec, it may be difficult to ensure a sufficientdeburring effect.

[0066] To increase the probability of collision of a water jet at a highpressure with burrs, the water jet may be discharged on both surfaces ofa yoke component. Since the surface of the yoke component is wet and isthereby liable to be rusted after water jet deburring, the yokecomponent may be desirable to be dried by using an oven or air blower.With this water jet deburring treatment, shearing burrs of 0.5 mm orless in thickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless cannot be removed by the prior art single water jet deburringtreatment.

[0067] Whisker-like burrs having fine roots, which are produced atfinely machined portions, such as threaded holes or recesses, uponcutting work of a yoke component, can be perfectly removed by the impactapplied by a water jet.

[0068] The water jet deburring apparatus has been described in(“Advanced Cleaning Technology Handbook”—Chapter II Physical CleaningMedia and Cleaning Method, Paragraph 2 Cleaning Method, Section 5 HighPressure Water Cleaning—, edited by Advanced Cleaning TechnologyHandbook Editorial Committee and published by K.K. Industrial TechnologyService Center, 1996).

[0069] If the water jet deburring treatment is performed without barrelpolishing as the previous step, as described above, shearing burrs whichhave roots wider than tips cannot be removed at the roots even if a highwater pressure is applied to the burrs, and therefore, shearing burrs onall ridge lines, including burrs at finely machined portions, cannot beremoved at all.

[0070] In rare cases, during the barrel polishing treatment as the firststep and the abrasive grain fluidization treatment or the like at secondstep, fine shearing burrs of 0.1 mm or less in thickness present atfinely machined portions of a yoke component may fall onto the main bodyof the yoke component to be in close-contact therewith. These burrscannot be perfectly removed by the first and second deburring steps. Inthese cases, it is effective to dissolve and remove the remaining burrsby a chemical polishing treatment as the finish step. The chemicalpolishing is performed by dipping a yoke component in a water solutionmainly containing 1 to 40% of hydrogen peroxide, ammonium hydrogendifluoride, or phosphoric acid for 10 sec to 10 min, thereby chemicallydissolving burrs on the yoke component.

[0071] Since the surface of the yoke component is activated afterchemical polishing, the yoke component may be desirable to beimmediately subjected to water washing and acid cleaning, and to nickelor copper plating. It should be noted that the abrasive grainfluidization treatment or the like at the second step, the chemicalpolishing treatment at the final step, and plating can be continuouslyperformed by commonly using a jig for fixing or suspending a yokecomponent.

[0072]FIGS. 3A to 3D typically show stages in which shearing burrsproduced at the opening edge of a through-hole are removed in the barrelpolishing treatment at the first step, the abrasive grain fluidizationtreatment or the like at the second step, and the additional chemicalpolishing treatment at the final step, wherein FIG. 3A shows a statebefore barrel polishing; FIG. 3b shows a state after barrel polishing;FIG. 3C shows a state after abrasive grain fluidization or the like asthe second step; and FIG. 3D shows a state after chemical polishing. Inthe figures, reference numeral 1 designates a main body of a yokecomponent, and 2 is a through-hole formed in the main body. In the statebefore barrel polishing, shown in FIG. 3A, a fine shearing burr 11 and ashearing burr 12 of 0.5 mm or less in thickness are formed at the outerperipheral edge of the through-hole 2 in such a manner as to projectoutwardly in the depth direction of the through-hole 2. Since the rootof each of the burrs 11 and 12 is wider than a tip thereof, such a burrcannot be removed only by the abrasive grain fluidization treatment orthe like as the second step. When the yoke component 1 having the burrs11 and 12 is subjected to barrel polishing (see FIG. 3B), an abrasivegrain 3 collides with the burrs 11 and 12, to press the burrs 11 and 12inwardly, that is, toward the inside of the through-hole 2. The barrelpolishing does not remove but roll the burrs 11 and 12, to thereby makethin the roots thereof. As shown in FIG. 3B, the fine shearing burr 11may often fall on the inner peripheral wall of the through-hole 2, andin some cases, the tip side of the burr 11 may come in contact with theinner peripheral wall of the through-hole 2. The yoke component is thensubjected to the abrasive grain fluidization treatment or the like asthe second step. At this time, as shown in FIG. 3C, since the roots ofthe burrs 11 and 12 have been made thin by barrel polishing, the burrs11 and 12 are removed by the abrasive grain fluidization treatment orthe like as the second step. In this case, there is a possibility thatthe fine shearing burr 11 having fallen on the inner peripheral wall ofthe through-hole 2 is not perfectly removed by the abrasive grainfluidization treatment or the like as the second step. As shown in FIG.3D, such a remaining portion of the fine shearing burr 11 is perfectlyremoved by chemical polishing. It should be noted that the deburringstages appeared when the deburring method of the present invention iscarried out are not limited to those shown in FIGS. 3A to 3D.

[0073] With the above-described steps, it is possible to remove alllarge and small burrs, including shearing burrs of 0.5 mm or less inthickness present at finely machined portions, such as through-holes,bends, and threaded holes, of a yoke component for making up a magneticcircuit of a voice coil motor for a hard disk drive, which shearingburrs of 0.5 mm or less in thickness cannot be removed by the prior artsingle deburring step of subjecting the yoke component to any one of thebarrel polishing treatment, abrasive grain fluidization treatment,thermal deburring treatment, magnetic polishing treatment, ultrasonicdeburring treatment, and water jet deburring treatment. The yokecomponent, from which all the burrs have been removed, is thensubjecting to plating, to be thus finished as a yoke component of avoice coil motor in which the possibility of drop of burrs harmful for ahard disk drive is eliminated.

[0074] The yoke component of the present invention is thereforecharacterized in that burrs on all ridge lines, including burrs of 0.5mm or less in thickness present at finely machined portions, such asthrough-holes, threaded holes and recesses each of which has an diameterof 10 mm or less, and bends each of which has a radius of curvature of 5mm or less, of the yoke component are removed by the above-describeddeburring method of the present invention.

[0075] The voice coil motor of the present invention is thereforecharacterized by adhesively bonding a magnet to the yoke component ofthe present invention, followed by magnetization, and assembling theyoke component with other components. It should be noted that theconfigurations of other components of the voice coil motor in which theabove yoke component is assembled may be the same as thosepublicly-known.

EXAMPLES

[0076] The present invention will be more clearly understood by way of,while not limited thereto, the following examples:

Inventive Example 1

[0077] Yoke components, each having a weight of 30 g, for making upmagnetic circuits of voice coil motors for hard disk drives wereprepared by punching a cold-rolled steel sheet (grade: SPCC specified inJIS) of 3.2 mm in thickness. Each yoke component having a flat-shape ofabout 5 cm in diagonal length has two through-holes each having andiameter of 3 mm and one rolled tap having an diameter of 2.5 mm. Thesethrough-holes and rolled tap, which are opened in the thicknessdirection of the yoke component, are used for positioning the voice coilmotor to the hard disk drive upon assembly thereof. The yoke componenthas shearing burrs produced, upon punching of the yoke component, on allridge lines on the press-die side, including ridge lines of thethrough-holes (diameter: 3 mm), and also whisker-like burrs produced,upon thread-cutting of the rolled-tap (diameter: 2.5 mm), on a thread ofthe rolled tap. These yoke components are taken as test pieces. The testpieces were then subjected in sequence to a rotary barrel polishingtreatment and an abrasive grain fluidization treatment under thefollowing conditions:

[0078] Deburring Step by Rotary Barrel Polishing Treatment

[0079] charged amount of yoke components: 50 pieces×30 g

[0080] charged amount of spherical abrasive grains mainly made fromalumina or silica (outside diameter: 15 mm): 5 kg

[0081] number of revolution: 46 rpm

[0082] polishing time: 1 hr

[0083] Deburring Step by Abrasive Grain Fluidization Treatment

[0084] media: polymer base in which powder (particle size: #320specified in JIS) of silicon carbide is kneaded

[0085] pressure: 50 kg/cm²

[0086] pressing time for each side in reciprocating motion: 30 sec

[0087] number of reciprocating motion: one time

[0088] After barrel polishing, the two through-holes (diameter: 3 mm)and one rolled-tap (diameter: 2.5 mm) for each test piece were deburredfor 1 min in total by abrasive grain fluidization under the aboveconditions.

[0089] The test pieces thus deburred were subjected to nickel plating.The shearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-holes (diameter: 3 mm),and whisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 1.

[0090] For comparison, the following comparative test pieces wereprepared, and deburring states of the test pieces were evaluated in thesame manner as described above.

Comparative Example 1

[0091] The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

[0092] The test pieces were subjected to the above-described barrelpolishing treatment and a chemical polishing treatment.

Comparative Example 3

[0093] The test pieces were subjected only to the above-describedabrasive grain fluidization treatment.

[0094] The chemical polishing treatment was performed by diluting achemical polishing solution mainly containing hydrogen peroxide orammonium hydrogen difluoride (CPL-100, produced by Mitsubishi GasChemical Company, Inc.) by three times, and dipping each test piece inthe chemical polishing solution kept at 20° C. for 1 min.

[0095] The results are shown in Table 1. TABLE 1 ridge line at edgeridge line in ridge line on of through-hole rolled-tap state of outerperiphery (diameter: 3 mm) (diameter: 2.5 mm) burr shearing burrshearing burr whisker-like burr Inventive ˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ⊚Example 1 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm x ˜0.1mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm ∘˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm x ˜0.1mm x ˜0.1 mm ⊚ Example 3 0.1 to x 0.1 to x 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm

[0096] In Inventive Example 1, the test pieces were subjected tochemical polishing after abrasive grain fluidization treatment. As aresult, the shearing burrs of 0.1 mm or less shown in Table 1 wereperfectly removed.

Inventive Example 2

[0097] The same test pieces as those used in Inventive Example 1 weresubjected in sequence to a rotary barrel polishing treatment and athermal deburring treatment in the following conditions:

[0098] Deburring Step by Rotary Barrel Polishing Treatment

[0099] charged amount of yoke components: 50 pieces×30 g

[0100] charged amount of spherical abrasive grains mainly made fromalumina or silica (outside diameter: 15 mm): 5 kg

[0101] number of revolution: 46 rpm

[0102] polishing time: 1 hr

[0103] Thermal Deburring Treatment

[0104] composition of combustion gas: CH₄:O₂=1:2.5

[0105] charging pressure of mixed gas: 7.0 kg/cm²

[0106] charged amount of yoke components: 150 pieces

[0107] The test pieces thus deburred were subjected to nickel plating.The shearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 2.

[0108] For comparison, the following comparative test pieces wereprepared, and deburring states of the test pieces were evaluated in thesame manner as described above.

Comparative Example 1

[0109] The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

[0110] The test pieces were subjected to the above-described barrelpolishing treatment and the chemical polishing treatment.

Comparative Example 4

[0111] The test pieces were subjected only to the above-describedthermal deburring treatment.

[0112] The chemical polishing treatment was performed in accordance withthe same manner as that described in Inventive Example 1.

[0113] The results are shown in Table 2. TABLE 2 ridge line at edgeridge line in ridge line on of through-hole rolled-tap state of outerperiphery (diameter: 3 mm) (diameter: 2.5 mm) burr shearing burrshearing burr whisker-like burr Inventive ˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ⊚Example 2 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm x ˜0.1mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm ∘˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm x ˜0.1mm x ˜0.1 mm ⊚ Example 4 0.1 to x 0.1 to x 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm

[0114] In Inventive Example 2, the test pieces were subjected tochemical polishing after thermal deburring treatment. As a result, theshearing burrs of 0.1 mm or less shown in Table 2 were perfectlyremoved.

Inventive Example 3

[0115] The same test pieces as those used in Inventive Example 1 weresubjected in sequence to a rotary barrel polishing treatment and amagnetic polishing treatment in the following conditions:

[0116] Deburring Step by Rotary Barrel Polishing Treatment

[0117] charged amount of yoke components: 50 pieces×30 g

[0118] charged amount of spherical abrasive grains mainly made

[0119] from alumina or silica (outside diameter: 15 mm): 5 kg

[0120] number of revolution: 46 rpm

[0121] polishing time: 1 hr

[0122] Magnetic Polishing Treatment

[0123] material of media: SUS304 (specified in JIS)

[0124] shape of media: φ0.5×5L (mm)

[0125] charged amount of media: 1 kg

[0126] dimension of vessel: φ300×150H (mm)

[0127] Under the above conditions, each yoke component was fixed to aTeflon made jig in an upright state in the vessel and the media andwater were put in the vessel, and then the media was stirred andvibrated by alternately changing N and S poles of a magnetic field at 60Hz for 10 min.

[0128] The test pieces thus deburred were subjected to nickel plating.The shearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 3.

[0129] For comparison, the following comparative test pieces wereprepared, and deburring states of the test pieces were evaluated in thesame manner as described above.

Comparative Example 1

[0130] The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

[0131] The test pieces were subjected to the above-described barrelpolishing treatment and the chemical polishing treatment.

Comparative Example 5

[0132] The test pieces were subjected only to the above-describedmagnetic polishing treatment.

[0133] The chemical polishing treatment was performed in accordance withthe same manner as that described in Inventive Example 1.

[0134] The results are shown in Table 3. TABLE 3 ridge line at edgeridge line in ridge line on of through-hole rolled-tap state of outerperiphery (diameter: 3 mm) (diameter: 2.5 mm) burr shearing burrshearing burr whisker-like burr Inventive ˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ⊚Example 3 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm x ˜0.1mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm ∘˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm x ˜0.1mm x ˜0.1 mm ⊚ Example 5 0.1 to x 0.1 to x 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm

[0135] In Inventive Example 3, the test pieces were subjected tochemical polishing after magnetic polishing treatment. As a result, theshearing burrs of 0.1 mm or less shown in Table 3 were perfectlyremoved.

Inventive Example 4

[0136] The same test pieces as those used in Inventive Example 1 weresubjected in sequence to a rotary barrel polishing treatment and anultrasonic deburring treatment in the following conditions:

[0137] Deburring Step by Rotary Barrel Polishing Treatment

[0138] charged amount of yoke components: 50 pieces×30 g

[0139] charged amount of spherical abrasive grains mainly made fromalumina or silica (outside diameter: 15 mm): 5 kg

[0140] number of revolution: 46 rpm

[0141] polishing time: 1 hr

[0142] Ultrasonic Deburring Treatment

[0143] frequency of ultrasonic waves: 25 kHz

[0144] output of ultrasonic waves: 1,200 W

[0145] water temperature: 10° C.

[0146] water quality: pure water

[0147] Under the above conditions, each yoke component was suspended byusing a wire, and was subjected to ultrasonic deburring for 1 min whilebeing swung in the vertical direction.

[0148] The test pieces thus deburred were subjected to nickel plating.The shearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 4.

[0149] For comparison, the following comparative test pieces wereprepared, and deburring states of the test pieces were evaluated in thesame manner as described above.

Comparative Example 1

[0150] The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

[0151] The test pieces were subjected to the above-described barrelpolishing treatment and the chemical polishing treatment.

Comparative Example 6

[0152] The test pieces were subjected only to the above-describedultrasonic deburring treatment.

[0153] The chemical polishing treatment was performed in accordance withthe same manner as that described in Inventive Example 1.

[0154] The results are shown in Table 4. TABLE 4 ridge line at edgeridge line in ridge line on of through-hole rolled-tap state of outerperiphery (diameter: 3 mm) (diameter: 2.5 mm) burr shearing burrshearing burr whisker-like burr Inventive ˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ⊚Example 4 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm x ˜0.1mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm ∘˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm x ˜0.1mm x ˜0.1 mm ⊚ Example 6 0.1 to x 0.1 to x 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm

[0155] In Inventive Example 4, the test pieces were subjected tochemical polishing after ultrasonic deburring treatment. As a result,the shearing burrs of 0.1 mm or less shown in Table 4 were perfectlyremoved.

Inventive Example 5

[0156] The same test pieces as those used in Inventive Example 1 weresubjected in sequence to a rotary barrel polishing treatment and a waterjet deburring treatment in the following conditions:

[0157] Deburring Step by Rotary Barrel Polishing Treatment

[0158] charged amount of yoke components: 50 pieces×30 g

[0159] charged amount of spherical abrasive grains mainly made fromalumina or silica (outside diameter: 15 mm): 5 kg

[0160] number of revolution: 46 rpm

[0161] polishing time: 1 hr

[0162] Water Jet Deburring Treatment

[0163] bore diameter of nozzle: 0.3 mm (direct-jet type)

[0164] discharge pressure: 500 kg/cm²

[0165] distance between nozzle and yoke component: 50 mm dischargedamount of high pressure water: 20 L/min

[0166] discharge time of high pressure water: 2 sec

[0167] Under the above conditions, the nozzle was positioned to each ofthe two through-holes (diameter: 3 mm) and one rolled tap (diameter: 2.5mm), and each of the through-holes and rolled tap was deburred by awater jet for 2 sec.

[0168] The test pieces thus deburred were subjected to nickel plating.The shearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 5.

[0169] For comparison, the following comparative test pieces wereprepared, and deburring states of the test pieces were evaluated in thesame manner as described above.

Comparative Example 1

[0170] The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

[0171] The test pieces were subjected to the above-described barrelpolishing treatment and the chemical polishing treatment.

Comparative Example 7

[0172] The test pieces were subjected only to the above-described waterjet deburring treatment.

[0173] The chemical polishing treatment was performed in accordance withthe same manner as that described in Inventive Example 1.

[0174] The results are shown in Table 5. TABLE 5 ridge line at edgeridge line in ridge line on of through-hole rolled-tap state of outerperiphery (diameter: 3 mm) (diameter: 2.5 mm) burr shearing burrshearing burr whisker-like burr Inventive ˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ⊚Example 5 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm x ˜0.1mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5 to ⊚0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm ⊚ ˜0.1 mm ∘˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5 mm 0.5 mm 0.5to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1 mm x ˜0.1mm x ˜0.1 mm ⊚ Example 7 0.1 to x 0.1 to x 0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm

[0175] In Inventive Example 5, the test pieces were subjected tochemical polishing after water jet deburring treatment. As a result, theshearing burrs of 0.1 mm or less shown in Table 5 were perfectlyremoved.

[0176] As described above, the deburring method of the present inventionis effective to remove burrs on all ridge lines, including burrs onridge lines at finely machined portions, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, andtherefore, such a method is also effective to manufacture a clean voicecoil motor from which burrs harmful to a hard disk drive are removed.

[0177] While the preferred embodiments of the present invention havebeen described using the specific terms, such description is forillustrative purposes only, and it is to be understood that changes andvariations may be made without departing from the spirit or scope of thefollowing claims.

1. A deburring method of removing burrs present on the surface of a yokecomponent, made from a low steel carbon steel, of a voice coil motor fora hard disk drive, comprising: a first step of subjecting said yokecomponent to a barrel polishing treatment; and a second step ofsubjecting said yoke component to at least one of an abrasive grainfluidization treatment, a thermal deburring treatment, a magneticpolishing treatment, an ultrasonic deburring treatment, and a water jetdeburring treatment.
 2. A deburring method according to claim 1, furthercomprising a third step of subjecting said yoke component to a chemicalpolishing treatment.
 3. A deburring method according to claim 1, whereinthe thickness of each of said burrs to be removed by said steps is in arange of 0.5 mm or less.
 4. A deburring method according to claim 1,wherein said burrs have been produced by shearing work upon manufactureof said yoke component.